coil pack..new fuel pump..faulty fuel pressure regulator or injector

Customer Question

Hi my car is having some problems when i start it it starts after a few seconds it sounds like it wants to die out but then goes back regular idle I have to give it some gas in order to go to regular idle it only does that when i start it when im driving it its fine.Ive replaced the coil pack the ignition control module it has a new fuel pump and filter new spark plugs and new throttle control sensor could it be a faulty fuel pressure regulator or injector I dont know let me know what you think I really need some help thank you Christian Santos.

Hello Mr.Aguirre, you may have a dirty throttle body, or a sticking or defective idle air control valve. You can clean the throttle body and throttle plate with a cleaner made for this, use and old tooth brush to clean both side sides the plate, then wipe out with a rag. You can remove the IAC valve and give it a cleaning also. If you still have the problem,replace the IAC valve. Here are some illustrations .I hope this helps ,Jerry.

Hello Mr Aguire,sorry to hear that the IAC and cleaning didn't fix your problem. I did some searching for similar problems on your model car and found many reasons for the idle problem. You didn't say if it happens only cold or at all times. If cold I found that things like a vacuum leak,to high oil pressure causing pumped up lifters have been found. I will send one of the help requests and what was found.It turned out to be a rare problem that took some time to find. To check your problem out further would require some in depth testing with a scan tool, to check the sensors and fuel trims when this problem occurs. Sorry what I suggested didn't help,it does cure the problem 90% of the time, sending this to try to help you get some direction to the car fixed,no need to hit accept again, Jerry.

Argh! This vehicle has been driving me nuts for the lastcouple of days. The problem is it only acts up veryintermitantly with NO CODES... What happens is after theengine warms up to operating temperature it will begin tostall/cut out down to 300rpm then recover to 900rpm then stalldown to 300rpm and repeat indefinatly. It will do it after acontinuous run from cold to warm, or from a warm restart after30min-1hour after a shutdown. Cannot perdict when it will doit. You can rev the engine up to 2000rpm and you can stillfeel a slight mis and the engine will buck periodically.

With the engine acting normally I drove it on the highway anddoing 100Kph(55mph) and mashine the accelerator there is nopickup, just a lot of noise, you have to manually shift thetrany (auto) and you hear what sounds like an exhaust leakwhen the engine is reved above 4500rpm under load only. Thereis some acceleration but nothing to write home about. There isbetter part throttle acceleration at these speeds than at WOT.

I disconnected the iac with the engine idling normally at900rpm and drove it throught he city with multiple stops andstarts with a 45minute shutdown and restart with no problem.The engine did stall after it sat and cooled down and tried tofast idle(3 hour cooling with outside temp at 6^C (44^F).

There is oil leaking from the cam cover and from around theoil presure sensor boss.

At the time I hooked the scan tool up to it, it behavedperfectly for over an hour of trying to get it to misbehave.Even when the idle is surgine the alternator is putting out13.8V+ at 300rpm, Here is what I have for the only real scansession:

I have looked at tons of iatn posts from Oil pressure totiming belt skipping to reflashing the comp. I'm not reallyinto throwing parts at vehicle untill i'm entirely desperate,I'm not there...yet! I know iatn's experiance will let me makethe correct choices and repairs.

Thanks in advance, I'll update when I obtain some morerelavent information.

Matthew

___________________ TEST AND REPAIR DATA ___________________

Checked for codes and none were found.

RELATED REPAIR HISTORY

Replaced IAC with known good unit with no change indrivability. Replaced Ignition Boots, Plugs Were ReplacedThree Years and 40K ago.

______________ COMMENTS ADDED ON Dec 29, 2007 ______________

Thanks For Your Patience. This vehicle came in for unrelatedmintenance and we did the back pressure test. It was perfect.At idle the gauge was below 0.25psi, at 2000rpm the gauge wasaround 0.25psi, and at 4000rpm the gauge was between 0.25psi &0.50psi. This was done at operating temperature, before andafter the cat, and with the engine running perfectly...for an11year old quad4!

The noise that is being heard is from the balance shaft chain.The chain tensioner was broken causing it to vibrate and makethis noise.

Thanks again for all who replied Matthew

____________________________ FIX ___________________________

Thanks to all who replied, I'm with the majority and believethat there is also an exhaust restriction, but after thevehicle was repaired the customer chose to take the vehicleand has not returned yet for the back pressure test.

The problem turned out to be a faulty diode within thealternator. WHen I looked throught he other IATN posts, othershave had leaking AC current drivability problems. I hooked myDVOM between the positive battery terminal and alternator caseand recorded these reaedings before replacing. At idle beforethe car would surge and idle rough there was 0.050V of ACcurrent. when the idle began getting rough and cylinders wouldstart to drop out the AC volts went up to 0.100V, when thevehicle started to surge the AC Volts whent up to 0.200V, andwhen the vehicle would stall the AC volts would rise up to0.355-0.400AC-V before the engine stalled out. The quality ofthe idle was in direct proportion to the amount of AV Currentbeing produced. If I get the vehicle back to do a backpressure test I'll update this post with the readings.

Reply to Roadside Jerry's Post: Hi jerry is Christian my car still does it if its cold or hot thats why I give it a little gas when I start it then it goes back to normal idle.I change the IAC like you said and cleaned the throttle still does the same thing you think it could be fuel pressure or a bad injector I should take it to get scan,you think a pontiac dealer will tell me what it is whats your opinion thanks for responding get back to me when you can thanks.

Hello Christian, It could be that the fuel pressure is bleeding of when you shut the engine off. A fuel pressure test would show this. It can be an injector that leaks down or the check valve in the fuel pump. It can also be a pressure regulator that leaks fuel into the vacuum hose. The only way to find the problem is with some testing,it could take around 2 hours to do all the tests that would be needed, they idea is to check the systems involved ,to prove what is working correctly and what is out of specs This will save you from just replacing parts ,hoping to find the problem. A dealer may be a good place to go, or i you can try to find an independent shop that does this type work, If you want to try to find one ,I suggest you look into WWW.IATN.net ,there is a shop finder on the website, on the left side,says Having Car Problems, look to see if there is a member shop in your area, If so or if you go to a dealer, explain to them your exactly what the problem is. You would have to leave the car so they can test it, to feel what is happening. I hope this helps you to get it repaired. Let me know what is found, or if you need any more questions answered on this problem, this question will remain open for you to come back to. Good luck,Jerry.

Reply to Roadside Jerry's Post: Ok jerry im just gonna take it to a shop instead and have them check it out thanks for all your help hey one more thing theres times when I start my vehicle theres a nocking noise coming from the engine it nocks three times and goes away I dont know what it could be any idea?

Hello Mr Aguirre, a knock or clicking that goes away after a very short time is usually an oil drain back problem. I would try using the correct AC brand oil filter,since some other brand filters tend to drain back oil out of the filter.This causes a delay for the oil presuure to build up. I would also switch to a 10 w30 oil if you are presently using a 5w30. Thanks for accepting,good luck with the car,Jerry.

Thanks for getting back jerry its funny I been always using a fram oil filter and before I never had that nocking noise before thats kinda od to tell you the truth Im ready to sell my car lol!Well thanks for the info jerry.

Share this conversation

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.

JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.

I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry.Stephanie PElm City, NC

I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry.Stephanie PElm City, NC

used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will
recommend you and use you in the future.David L.Richmond, TX

9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. PhilMarysville, CA

Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible.CharlesWalnut Creek, CA

As a single woman, I really appreciate an excellent and affordable opinion. Thank you Geordie, I will not hesitate to contact justanswer in the future!SueCharleston, WV

Another great insight to what may be the problem. I will
have my mechanic take a look at it tomorrow. Thanks again, Frank...you do indeed know your stuff. JimCastleberry, FL

Excellent reply, and also very quick. Really sounds like the Expert knows what he is talking about. I will be back to use your service when I need more help with my RV.DutchUSA

Ask an Auto Mechanic

Get a Professional Answer. 100% Satisfaction Guaranteed.

60 Auto Mechanics are Online Now

Type Your Car Question Here...

characters left:

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.